A printing plate is ordinarily prepared by imagewise exposing and developing a planographic printing plate material. As a developer used for developing the planographic printing plate material is used an aqueous alkali solution or an organic solvent. This has problem in safety and sanitation. Further, there is problem of environmental pollution in disposal of the developer waste.
In order to solve the above problems, a planographic printing plate material capable of being developed with water is disclosed in Japanese Patent O.P.I. Publication Nos. 58-2847, 58-49940, 58-2830, and 58-2834 which comprises a diazo resin and a water-softening polymer.
As a planographic printing plate material capable of developing with water on a press, there is a planographic printing plate material disclosed in U.S. Pat. Nos. 4,879,201, 4,916,041, 4,999,273, and 5,258,263, and JP-A-8-506191 and JP-A-8-507163, which comprises developing agent-contained microcapsules formed on a polymer resist or dispersed in a polymer resist; or a planographic printing plate material disclosed in JP-A-10-500915 which comprises a development stabilizing agent capable of forming a hydrogen bond. These can be used as a countermeasure to solve the above problems.
In Japanese Patent O.P.I. Publication Nos. 9-123387 and 9-123388 are disclosed a planographic printing plate material is disclosed which comprises an image formation layer containing hydrophobic thermoplastic polymer particles capable of being heat fused and a planographic printing plate material which comprises an image formation layer containing light-to-heat conversion materials, and a developing process on a press of these planographic printing plate materials. These propose a counter measure to solve the above problems and provide technique suitable for recent tendency to the digitization.
There are several Patent documents described regarding a developing process on a press of a planographic printing plate material capable of being developed on press. A process is disclosed in Japanese Patent O.P.I. Publication Nos. 9-123387 and 9-123388, which comprises the steps of providing, on a plate cylinder of a press, an image formation element with recorded image capable of being developed on a press; supplying dampening water to the element by contacting the element with a dampening roller; after ten rotations of the cylinder, supplying ink to the element by contacting the element with an inking roller; and after further ten rotations of the cylinder, providing a print with no stain at non-image portions.
However, this process is insufficient in development. For example, although no stain occurs at non-image portions at an initial printing stage, there is problem in that there occurs block (so-called filling-up) at high image density portions such as shadow portions, which is difficult to obtain prints with good image quality.
In Japanese Patent O.P.I. Publication No. 2000-52634, is disclosed a developing process on a press as described below.
The process is one in which a planographic printing plate material capable of being developed with water or of being developed on a press is developed on an off-set printing press according to the following procedure to prepare a planographic printing plate. The procedure comprises the steps of 1) imagewise heating or imagewise exposing a planographic printing plate material to form a recorded image on an image formation layer; 2) providing the printing plate material on a plate cylinder of a press; 3) supplying dampening water to the printing plate material by contacting a dampening roller with the printing plate material while rotating the plate cylinder, provided that an inking roller is not contacted with the printing plate material; and 4) transferring a part of the image formation layer to an image recording material (printing paper), whereby the planographic printing plate material is developed.
In this process, development of a planographic printing plate material is carried out by supply of dampening water and transfer of a part of the image formation layer to a printing paper, but it requires much time for development. This patent publication discloses that the supplied amount of dampening water supplied on development is 1.05 to 3.00 times the supplied amount of dampening water supplied during printing. However, it has been found that such an increase of the supplied amount of dampening water is insufficient to completely carry out development.
It has been found that it is necessary that after dampening water is supplied to a planographic printing plate material capable of being developed on a press, ink be supplied to the planographic printing plate material.
The present inventor has evaluated a planographic printing plate material capable of being developed on a press, varying the supplied amount of dampening water or inking roller nip timing, studied on conditions under which printing paper waste is reduced, and completed the invention.